Fuel tank

ABSTRACT

Disclosed herein is a fuel tank of multi-layer construction having good impact resistance as well as good barrier properties for gasoline, especially one containing methanol and MTBE. 
     The fuel tank comprises (a) inner and outer layers of high-density polyethylene, (b) intermediate layers of adhesive resin, and (c) a core layer of ethylene-vinylalcohol copolymer, with said core layer (c) being shifted to the inside. For better performance, the layer (c) has a thickness which satisfies the formula below. 
     
         0.005≦A/B≦0.13                               (1) 
    
     where A is the thickness of the layer (c), and 
     B is the thickness of all the layers. 
     The fuel tank is suitable especially for oxygen-containing gasoline.

This application is a Continuation of application Ser. No. 08/643,011,filed on May 3, 1996, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an automobile fuel tank which has goodimpact resistance as well as good impermeability to automobile fuel,especially gasoline blended with methanol or methyl t-butyl ether(MTBE).

2. Description of the Prior Art

Plastics fuel tanks are coming into general use. Most popular among themare those of single-layer type made of polyethylene. Their disadvantageis a comparatively high permeability to gasoline. Conventional measuresagainst this were sulfonation of the polyethylene tank (Japanese PatentPublication No. 23914/1971), fluorination of the polyethylene tank(Japanese Patent Publication Nos. 21877/1972 and 15862/1978), andblending of polyethylene with nylon as a barrier material (JapanesePatent Laid-open No. 296331/1992). There has also been proposed aplastics fuel tank of five-layer construction in which the inner andouter layers are made of high-density polyethylene and the middle layeris made of nylon and they are bonded together with adhesive resinlayers.

It has been found that these prior art technologies do not cope with therecent situation arising from the use of the gasoline which containsoxygenated compounds such as methanol, ethanol or MTBE (referred to asoxygen-containing gasoline hereinafter) which started in the U.S. toprevent air pollution, to reduce gasoline consumption, to improve theoctane number of gasoline, and to lower the amount of unburnthydrocarbon in exhaust gas. Unfortunately, the above-mentionedsulfonation or fluorination of the single-layered polyethylene fuel tankdoes not provide sufficient barrier properties for oxygen-containinggasoline. Likewise, the combination of nylon with polyethylene (in theform of multi-layer or dispersion) does not completely preventpermeation of oxygen-containing gasoline through the fuel tank.

To address this problem, there has been proposed a multi-layer fuel tankcomposed of polyethylene and ethylene-vinyl alcohol copolymer (EVOH forshort hereinafter) which exhibits good gasoline barrier properties.Although it is superior in barrier properties to the conventional fueltanks, there still is room for improvement to meet the futureenvironmental regulations. Improvement in impact resistance is anothersubject to be considered.

One way to approach problems involved in the fuel tank having anintermediate layer of EVOH is by blending EVOH with polyolefin orpolyamide (as proposed in Japanese Patent Laid-open Nos. 218891/1994 and52333/1995). However, the problems still remain unsolved because suchblending appreciably impairs the gasoline barrier properties andadversely affects the melt stability of the raw material.

SUMMARY OF THE INVENTION

The present invention was completed in view of the foregoing. It is anobject of the present invention to provide a multi-layered fuel tankcomposed of high-density polyethylene and EVOH layers, which is superiorin gasoline barrier properties (especially for oxygen-containinggasoline) and impact resistance.

This object could be achieved on the basis of the surprising findingthat a fuel tank of multi-layer construction which comprises (a) innerand outer layers of high-density polyethylene, (b) intermediate layersof adhesive resin, and (c) a core layer of ethylene-vinyl alcoholcopolymer shows the above-mentioned desired properties if the totalthickness of the layers positioned inside the layer (c) is smaller thanthe total thickness of the layers positioned outside of the layer (c).

According to a preferred embodiment of the present invention, the layer(c) has a thickness which satisfies the formula below.

    0.005≦A/B≦0.13                               (1)

where A is the thickness of the layer (c), and

B is the thickness of all the layers.

The present invention especially produces its noticeable effect when thefuel tank is used for gasoline comprising oxygene-containing compounds.

According to the present invention, the multi-layer construction ischaracterized in that the total thickness of the layers positionedinside the layer (c) is smaller than the total thickness of the layerspositioned outside of the layer (c). This arrangement contributes to thesuperior barrier properties (especially for oxygen-containing gasoline)and good impact resistance. These characteristics make the fuel tank tomeet the environmental and safety regulations. The multi-layerconstruction provides as good barrier properties and impact resistanceas the conventional one even though the EVOH layer is reduced inthickness. This leads to cost reduction and thickness reduction (andhence weight reduction)

These effects are enhanced when the formula (1) above is satisfied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The fuel tank of the present invention is constructed of (a) inner andouter layers of high-density polyethylene, (b) intermediate layers ofadhesive resin, and (c) a core layer of ethylene-vinyl alcoholcopolymer. It is extremely important in the present invention that theratio (I/O) is smaller than 50/50, where I is the total thickness of thelayers positioned inside of the layer (c), and O is the total thicknessof the layers positioned outside of the layer (c), in other words thatthe core layer (c) is shifted to the inside of the fuel tank wall.

(Incidentally, the thickness of each layer is an average measured at thebulge of the fuel tank.)

Shifting the EVOH layer (c) to the inside improves the gasoline barrierproperties and impact resistance, as demonstrated in Example 1 andComparative Examples 3 to 5. It is to be noted that the value ofgasoline barrier properties is increased more than four-fold by movingthe EVOH layer (c) from the outermost position (as in ComparativeExample 5) to the innermost position (as in Comparative Example 3), withthe layers (a), (b), and (c) being the same in thickness. It is alsonoted that the value of gasoline barrier properties is increased about1.5-fold by moving the EVOH layer (c) from the center (as in ComparativeExample 4) to the position where the ratio (I/O) is 20/80 (as in Example1). It is significant that the performance of the fuel tank ofmulti-layer construction greatly varies as mentioned above although thematerials and their amount are substantially the same.

The reason for the above-mentioned effect of improving gasoline barrierproperties is not known. It is believed that the degree of swelling ofthe high-density polyethylene layer (a) and EVOH layer (c) due togasoline, methanol, and MTBE varies depending on the position of theEVOH layer (c).

Also, shifting the EVOH layer (c) to the inside improves the impactresistance of the fuel tank, as demonstrated in Example 1 andComparative Example 4. That is, the height for breakage in drop test is5.7 m in the case where the EVOH layer (c) is positioned at the center(as in Comparative Example 4), whereas the height for breakage in droptest is increased to 7.6 m in the case where the EVOH layer (c) isshifted to the position where the ratio (I/O) is 20/80 (as in Example1). Presumably, the improvement in impact resistance is due to the soft,thick HDPE layer placed outside. Incidentally, although shifting theEVOH layer (c) to the inside improves the impact resistance of the fueltank, there is an optimum position for the most desired effect.

As mentioned above, shifting the EVOH layer (c) to the inside improvesthe gasoline barrier properties and impact resistance of the fuel tank.The greater the distance of shifting, the better the result. Thus, theposition for shifting should be such that the ratio (I/O) is equal to orsmaller than 45/55, preferably 40/60, more preferably 35/65, and mostdesirably 30/70.

According to the present invention, the fuel tank of multi-layerconstruction comprises (a) inner and outer layers of high-densitypolyethylene, (b) intermediate layers of adhesive resin, and (c) a corelayer of ethylene-vinyl alcohol copolymer. The core layer (c) should beshifted to the inside but should not be at the innermost position. Inother words, the innermost layer should be the high-density polyethylenelayer (a). The reason for this is that the fuel tank is usually formedby extrusion blow molding which involves the step of pinching-off theparison. So as to form a strong bottom, the parison should be closedwith good adhesion.

Thus, the position for shifting should be such that the ratio (I/O) isequal to or greater than 1/99, preferably 2/98, more preferably 5/95,and most desirably 10/90.

Also, the present invention produces its noticeable effect when the EVOHlayer (c) has a thickness which satisfies the formula below.

    0.005≦A/B≦0.13                               (1)

where A is the thickness of the layer (c), and

B is the thickness of all the layers.

If the ratio (A/B) is smaller than 0.005, the EVOH layer (c) would betoo thin to produce the desired gasoline barrier properties and would beuneven in thickness. The ratio (A/B) should be greater than 0.01,preferably greater than 0.02. If the ratio (A/B) is greater than 0.13,the EVOH layer (c) would be thicker than necessary (which leads to costincrease) and have an adverse effect on impact resistance. Therefore,the ratio (A/B) should be smaller than 0.10, preferably smaller than0.07.

The EVOH used in the present invention is one which is obtained bysaponification of an ethylene-vinyl ester copolymer. It should containethylene units in an amount of 20-60 mol %. With an amount less than 20mol %, it is poor in moldability and gasoline barrier properties underthe high-humidity condition. A preferred amount is more than 25 mol %and a more preferred amount is more than 30 mol %. Conversely, with anamount in excess of 60 mol %, it is poor in gasoline barrier properties.A preferred amount is less than 50 mol % and a more preferred amount isless than 40 mol %.

A typical example of the vinyl ester is vinyl acetate. It is possible touse other fatty acid vinyl esters, such as vinyl propionate and vinylpivalate.

The EVOH may contain additional comonomers in an amount not harmful tothe effect of the present invention. For example, the EVOH may beincorporated with 0.0002-0.2 mol % of vinyl silane compound so that theresulting EVOH has the same melt viscosity as the base resin forcoextrusion. The consequence is uniform coextrusion for multiple layersand good blending performance. Examples of the vinyl silane compoundinclude vinyltrimethoxysilane, vinyltriethoxysilane,vinyltri(-methoxyethoxy)silane, and 3-(trimethoxysilyl)propylmethacrylate. Of these examples, the first two are desirable. Additionalexamples of the comonomer include propylene, butylene, unsaturatedcarboxylic acids and esters thereof (such as (meth)acrylic acid and(meth)acrylate ester), and vinyl pyrrolidone.

The EVOH used in the present invention should have a melt index (MI) inthe range of 0.1-50 g/10 min, preferably 0.5-20 g/10 min, at 190° C.under a load of 2160 g. For samples having a melting point in theneighborhood of or in excess of 190° C., measurements are carried out atseveral points above the melting point under a load of 2160 g, and themelt index is determined by extrapolating the measured values to 190° C.on a semilogarithmic graph, with the reciprocal of the absolutetemperature on the abscissa of ordinary scale and the melt index on theordinate of logarithmic scale.

There may be an instance where a better result is obtained when EVOH isblended with one or more than one kind of other EVOH which differs inthe content of ethylene and/or the degree of hydrolysis.

The EVOH layer (c) in the present invention should essentially be madeof EVOH alone; however, the present invention does not preclude blendingEVOH with any other resin in an amount not harmful to its effect.Examples of such resins include polyolefin resin, polystyrene, polyamideresin, saturated polyester resin (such as polyethylene terephthalate),polycarbonate resin, polyvinyl chloride resin, and polyvinylidenechloride resin. Additional desirable examples include ethylene-acrylateester-maleic anhydride terpolymer and modified polyolefin having atleast one functional group selected from boronic acid group, borinicacid group, and boron-containing group convertible into boronic acidgroup or borinic acid group in the presence of water. The amount of theblending resin should be limited in consideration of gasoline barrierproperties and melt stability.

The high-density polyethylene used for layer (a) in the presentinvention is one which is obtained by the low-pressure process ormedium-pressure process which employs the Ziegler catalyst. It shouldhave a density higher than 0.93 g/cm³, preferably higher than 0.94g/cm³. With a density lower than 0.93 g/cm³, the high-densitypolyethylene is so poor in gasoline barrier properties and stiffnessthat it cannot be used for the fuel tank. The high-density polyethyleneshould also have a melt index in the range of 0.001-0.6 g/10 min,preferably 0.005-0.1 g/10 min (measured at 190° C. under a load of 2160g).

The high-density polyethylene for layer (a) may be incorporated withother resins in an amount not harmful to the effect of the presentinvention. Examples of such resins include polyolefin resin (other thanpolyethylene), polystyrene, polyamide resin, saturated polyester resin(such as polyethylene terephthalate), polycarbonate resin, polyvinylchloride resin, and polyvinylidene chloride resin.

Scraps resulting from molding or recovered from consumers may berecycled. Recycling of such scraps is desirable for environmentalprotection and cost reduction. Scraps may be used alone or incombination with virgin high-density polyethylene to form the layer (a).Alternatively, it is possible to form the layer (a) from the blend ofvirgin high-density polyethylene and recycled scraps.

Recovered scraps are usually composed of high-density polyethylene (as amajor component), EVOH resin, and adhesive resin. They may beincorporated with a compatibilizer and stabilizer so as to improve themoldability. Examples of the compatibilizer and stabilizer includeethylene-acrylate ester-maleic anhydride terpolymer, modified polyolefinhaving at least one functional group selected from boronic acid group,borinic acid group, and boron-containing group convertible into boronicacid group or borinic acid group in the presence of water, metal salt ofhigher fatty acid, and hydrotalcite.

The fuel tank of the present invention is formed by laminating thehigh-density polyethylene layers (a) on both sides of the EVOH layer(c), with the adhesive resin layer (b) placed between them. Theresulting fuel tank has outstanding gasoline barrier properties andimpact resistance. According to the preferred embodiment of the presentinvention, the high-density polyethylene layers (a) should be theinnermost layer and the outermost layer; however, they may be coveredwith a layer of any other resin so long as the object of the presentinvention is not hindered. The total thickness of the inner and outerhigh-density polyethylene layers (a) should be in the range of 300-10000μm, preferably 500-8000 μm, and most desirably 1000-6000 μm.

The adhesive resin used for the intermediate layer (b) is notspecifically restricted. It may be selected from modified polyolefinresin, polyurethane resin, and one-pack or two-pack polyester resin. Thefirst one (especially carboxylic acid-modified polyolefin resin) isdesirable from the standpoint of adhesion to EVOH and high-densitypolyethylene and moldability. It may be obtained by copolymerization orgrafting of olefin polymer with an unsaturated carboxylic acid oranhydride thereof (such as maleic anhydride). In this case, the olefinpolymer should preferably be polyethylene from the standpoint ofadhesion with high-density polyethylene and compatibility with recycledscraps. Examples of such carboxylic acid-modified polyethylene includethose which are obtained by modification with a carboxylic acid ofpolyethylene {such as low-density polyethylene (LDPE), linearlow-density polyethylene (LLDPE), super low-density polyethylene(SLDPE)}, ethylene-vinyl acetate copolymer, or ethylene-methyl or ethyl(meth)acrylate copolymer.

The adhesive resin layer (b) interposed between the high-densitypolyethylene layer (a) and the EVOH layer (c) contributes to goodinterlayer bonding for the fuel tank having good gasoline barrierproperties and impact resistance. The total thickness of the adhesiveresin layers (b) should be in the range of 5-1000 μm, preferably 10-500μm, and most preferably 20-300 μm. The adhesive resin layer would bepoor in adhesion properties if it is excessively thin. It would causecost increase if it is excessively thick.

The multi-layer construction for the high-density polyethylene layers(a), intermediate adhesive layers (b), and core EVOH layer (c) may berepresented as follows. In the case where the layers of recycled resinare included, they are indicated by "r".

5 layers:

(inside) a/b/c/b/a (outside), a/b/c/b/r, r/b/c/b/a

6 layers:

a/b/c/b/r/a, a/r/b/c/b/a, r/a/b/c/b/a, a/r/b/c/b/r,

r/a/b/c/b/r, a/b/c/b/a/r, r/b/c/b/r/a, r/b/c/b/a/r

7 layers:

a/r/b/c/b/r/a, a/r/b/c/b/a/r, r/a/b/c/b/a/r,

r/a/b/c/b/r/a, a/r/b/c/b/r/a, r/a/b/c/b/a/r

The above-listed layer construction is not limitative. Of theseexamples, a/b/c/b/a and a/b/c/b/r/a are desirable.

The total thickness of the fuel tank should be in the range of 310-10000μm, preferably 500-8500 μm, and most desirably 1000-7000 μm.(Incidentally, the thickness is an average value measured at the bulgeof the fuel tank.) An excessively large thickness leads to a heavy fueltank which is unfavorable for gas mileage and production cost. Anexcessively small thickness leads to a weak fuel tank due to lowstiffness. An adequate thickness should be selected according to thecapacity and intended use of the fuel tank.

The multi-layered fuel tank of the present invention may be produced inany manner which is not specifically restricted. Typical molding methodsinclude extrusion molding, blow molding, and injection molding, whichare commonly used in the field of polyolefins. Of these molding methods,coextrusion molding and coinjection molding are desirable, particularlycoextrusion blow molding is desirable.

The fuel tank of the present invention may be mounted on automobiles,motor cycles, vessels, aircraft, electric generators, and otherindustrial and agricultural machines. It may also be used as a portablecontainer or storage container.

The fuel tank may be used for gasoline and oxygen-containing gasoline(produced by blending gasoline with methanol and/or MTBE). It may alsobe used for other fuels such as heavy oil, gas oil, and kerosene. Itwill produce its desired effect when it is used for oxygen-containinggasoline.

Each layer may be incorporated with additives such asantioxidant,plasticizer, heat stabilizer, UV light absorber, antistaticagent, slip agent, colorant, and filler. Their respective examples aregiven below.

Antioxidant: 2,5-di-t-butylhydroquinone, 2,6-di-t-butyl-p-cresol,4,4'-thiobis-(6-t-butylphenol),2,2'-methylene-bis-(4-methyl-6-t-butylphenol),octadecyl-3-(3',5'-di-t-butyl-4'-hydroxyphenyl)propionate, and4,4'-thiobis-(6-t-butyiphenol). UV light absorber:ethylene-2-cyano-3,3'-diphenyl acrylate,2-(2'-hydroxy-5'-methylphenyl)benzotriazole,2-(2'-hydroxy-5'-methylphenyl)benzotriazole,2-(2'-hydroxy-5'-methylphenyl) benzotriazole,2-(2'-hydroxy-5'-methylphenyl)benzotriazole,2-(2'-hydroxy-3'-t-butyl-5'-methylphenyl)-5-chlorobenzotriazole,2-hydroxy-4-methoxybenzophenone, 2,2'-dihydroxy-4-methoxybenzophenone,and 2-hydroxy-4-ethoxybenzophenone.

Plasticizer: dimethyl phthalate, diethyl phthalate, dioctyl phthalate,wax, liquid paraffin, and phosphate ester.

Antistatic agent: pentaerythritol monostearate, sorbitan monopalmitate,sulfated polyolefins, polyethylene wax, and carbowax.

Slip agent: ethylene bis-stearamide and butyl stearate.

Colorant: carbon black, phthalocyanine, quinacridone, indoline, azodyes, and red oxide.

Filler: glass fiber, asbestos, wollastonite, calcium silicate, talc, andmontmorillonite.

For prevention of gel formation, the EVOH may be incorporated with anyone or more of hydrotalcite compounds, hindered phenol- or hinderedamine-heat stabilizers, and metal salt of higher fatty acid (such ascalcium stearate and magnesium stearate) in an amount of 0.01-1 wt %.

EXAMPLES

The invention will be described in more detail with reference to thefollowing examples and comparative examples, which are not intended tolimit the scope of the invention.

Example 1

A 500-ml container of five-layered construction was prepared bycoextrusion blow molding from high-density polyethylene (HDPE) for theinner and outer layers, adhesive resin (AD) for the intermediate layers,and EVOH for the core layer. The arrangement and thicknesses of thelayers are shown below.

inner HDPE/AD/EVOH/AD/outer HDPE

435/50/75/50/1890 μm

HDPE: "HZ8200B" from Mitsui Petrochemical Industries, Ltd.

MI=0.01 g/10 min (at 190° C. and 2160 g load)

density=0.96 g/cm³

EVOH: ethylene content=32 mol %

saponification degree=99.6%

MI=3.0 g/10 min (at 190° C. and 2160 g load)

AD: maleic anhydride modified polyethylene, "Admer GT4" from MitsuiPetrochemical Industries, Ltd.

MI=0.2 g/10 min (at 190° C. and 2160 g load)

This container was filled with 300 ml of model gasoline composed oftoluene (42.5 wt %), isooctane (42.5 wt %), and methanol (15 wt %). Withthe mouth tightly stoppered, the container was allowed to stand at 20°C. and 65% RH. The weight loss measured after 4 days was 0.33 g (anaverage of 6 samples).

The container was filled with water and the filled container was droppedon the concrete floor to test its impact resistance. The mean failureheight for 50% of the samples to break was 7.5 m. The mean failureheight was calculated according to Section 8 of JIS K7211 (a result of30 samples).

Examples 2 to 15 and Comparative Examples 1 to 12

The same procedure as in Example 1 was repeated except that the layerarrangement and layer thickness were changed as shown in Table 1. Theresults of the tests for barrier properties and impact resistance arealso shown in Table 1.

Example 16 and Comparative Example 13

The containers prepared in Example 1 and Comparative Example 4 weretested for barrier properties in the same manner as in Example 1, exceptthat the model gasoline was replaced by the one composed of toluene (50wt %) and isooctane (50 wt %), without methanol. The weight loss was0.02 g and 0.03 g, respectively.

Examples 17 to 20

The same procedure as in Example 1 was repeated except that the EVOH wasreplaced by the one with a different ethylene content. The results areshown in Table 2.

Example 21

The same procedure as in Example 1 was repeated except that the EVOH wasreplaced by the one modified with 0.01 mol % of trimethoxyvinylsilane.(ethylene content=47 mol %, degree of hydrolysis=96.0 mol %, MI=5.0 g/10min at 190° C. under a load of 2160 g). The weight loss was 0.73 g andthe mean failure height was 7.7 m.

Comparative Example 14

The same procedure as in Example 1 was repeated except that the EVOH wasreplaced by a resin blend (in pellet form) composed of 10 wt % of EVOHand 90 wt % of linear low-density polyethylene (LLDPE), both specifiedbelow.

EVOH: ethylene content=32 mol %

degree of hydrolysis=99.6 mol %

MI=3.0 g/10 min at 190° C. and 2160 g load

LLDPE "Ultzex 2022L" (from Mitsui Petrochemical Industries, Ltd.)

MI=2.1 g/10 min at 210° C. and 2160 g load The weight loss was 2.93 gand the mean failure height was 8.1 m.

Comparative Example 15

The same procedure as in Example 1 was repeated except that the EVOH wasreplaced by a resin blend (in pellet form) composed of 80 wt % of EVOHand 20 wt % of nylon-6 (PA-6), both specified below.

EVOH: ethylene content=32 mol %

degree of hydrolysis=99.6 mol %

MI=3.0 g/10 min at 190° C. and 2160 g load

Nylon-6: "Ube Nylon 1022B" from Ube Industries, Ltd.

MI=7.2 g/10 min at 230° C. and 2160 g load

The weight loss was 1.04 g and the mean failure height was 7.9 m.

Comparative Example 16

The same procedure as in Example 1 was repeated except that the HDPE wasreplaced by a linear low-density polyethylene (LLDPE) specified below.

LLDPE: "Ultzex 2022L" (from Mitsui Petrochemical Industries, Ltd.)

MI=2.1 g/10 min at 210° C. and 2160 g load density=0.920 g/cm³

The weight loss was 1.26 g and the mean failure height was 7.5 m. Theresulting sample was so poor in stiffness that it was easily deformedunder load.

Example 22

The same procedure as in Example 1 was repeated except that the adhesiveresin was replaced by "Bondyne TX 830" (from Atchem Co., Ltd.) which isa terpolymer composed of ethylene (60 wt %), acrylate ester (36 wt %),and maleic anhydride (4 wt %), having a melt index of 4.0 g/10 min (at190° C. under a load of 2160 g). The weight loss was 0.38 g and the meanfailure height was 7.3 m.

Example 23

The same procedure as in Example 1 was repeated except that the adhesiveresin was replaced by "EV270" (from Mitsui DuPont Polychemical Co.,Ltd.) which is an ethylene-vinyl acetate copolymer, having a melt indexof 4.0 g/10 min (at 190° C. under a load of 2160 g). The weight loss was0.37 g and the mean failure height was 6.2 m.

Example 24

The same procedure as in Example 1 was repeated except that the HDPE forthe inner layer was replaced by a recycled resin obtained by crashingand subsequent pelleting from the multi-layered container prepared inExample 1. The weight loss was 0.31 g and the mean failure height was6.9 m.

Example 25

The same procedure as in Example 1 was repeated except that the outerHDPE layer was formed in double layers. The outermost layer was formedfrom the same HDPE as used in Example 1. The adjacent layer was formedfrom a recycled resin obtained by crashing and subsequent pelleting fromthe multi-layered container prepared in Example 1. The ratio of thethickness of the outermost layer to the thickness of the adjacent layerwas 3:1. The weight loss was 0.32 g and the mean failure height was 6.5m.

                                      TABLE 1                                     __________________________________________________________________________                                       Mean                                                  Layer construction                                                                      Thickness                                                                          Thickness                                                                          Weight                                                                            failure                                               (a)/(b)/(c)/(d)/(e)                                                                     ratio                                                                              ratio                                                                              loss                                                                              height                                     Example No (μm)   (A/B)                                                                              (I/O)                                                                              (g) (m)                                        __________________________________________________________________________    Example 1  435/50/75/50/1890                                                                       0.03 20/80                                                                              0.33                                                                              7.6                                        Comparative Example 1                                                                    2500/0/0/0/0                                                                            0    --   3.13                                                                              8.6                                        Example 2  449/50/5/50/1946                                                                        0.002                                                                              20/80                                                                              2.24                                                                              7.9                                        Example 3  448/50/13/50/1940                                                                       0.005                                                                              20/80                                                                              1.66                                                                              7.8                                        Example 4  445/50/25/50/1930                                                                       0.01 20/80                                                                              0.92                                                                              7.3                                        Comparative Example 2                                                                    1188/50/25/50/1188                                                                      0.01 50/50                                                                              1.87                                                                              6.1                                        Comparative Example 3                                                                    0/0/75/50/2375                                                                          0.03  0/100                                                                             0.24                                                                              5.3                                        Example 5  23/50/75/50/2302                                                                        0.03  3/97                                                                              0.25                                                                              5.8                                        Example 6  47/50/75/50/2278                                                                        0.03  4/96                                                                              0.26                                                                              5.9                                        Example 7  71/50/75/50/2254                                                                        0.03  5/95                                                                              0.28                                                                              6.2                                        Example 8  193/50/75/50/2133                                                                       0.03 10/90                                                                              0.29                                                                              6.7                                        Example 9  678/50/75/50/1648                                                                       0.03 30/70                                                                              0.39                                                                              6.6                                        Example 10 969/50/75/50/1357                                                                       0.03 42/58                                                                              0.47                                                                              6.1                                        Comparative Example 4                                                                    1163/50/75/50/1163                                                                      0.03 50/50                                                                              0.49                                                                              5.7                                        Comparative Example 5                                                                    2375/50/75/0/0                                                                          0.03 100/0                                                                              1.06                                                                              4.7                                        Comparative Example 6                                                                    485/0/75/0/1940                                                                         0.03 20/80                                                                              0.87                                                                              3.6                                        Example 11 425/50/125/50/1850                                                                      0.05 20/80                                                                              0.11                                                                              6.8                                        Example 12 971/50/125/50/1304                                                                      0.05 43/57                                                                              0.15                                                                              5.5                                        Comparative Example 7                                                                    0/0/250/50/2200                                                                         0.10  0/100                                                                             0.03                                                                              4.1                                        Example 13 400/50/250/50/1750                                                                      0.10 20/80                                                                              0.04                                                                              6.2                                        Comparative Example 8                                                                    1300/50/250/50/850                                                                      0.10 60/40                                                                              0.06                                                                              4.1                                        Comparative Example 9                                                                    1930/50/250/50/220                                                                      0.10 88/12                                                                              0.12                                                                              3.9                                        Comparative Example 10                                                                   2200/50/250/0/0                                                                         0.10 100/0                                                                              0.22                                                                              3.8                                        Example 14 720/50/300/50/1380                                                                      0.12 35/65                                                                              0.04                                                                              4.6                                        Comparative Example 11                                                                   1050/50/300/50/1050                                                                     0.12 50/50                                                                              0.06                                                                              4.2                                        Example 15 350/50/500/50/1550                                                                      0.20 20/80                                                                              0.05                                                                              5.7                                        Comparative Example 12                                                                   950/50/500/50/950                                                                       0.20 50/50                                                                              0.08                                                                              3.6                                        __________________________________________________________________________

                  TABLE 2                                                         ______________________________________                                        Example No.                                                                           Ethylene content                                                                           Weight loss                                                                             Mean failure height                            ______________________________________                                        Example 17                                                                            27 mol %     0.29 g    7.2 m                                          Example 18                                                                            38 mol %     0.48 g    7.6 m                                          Example 19                                                                            44 mol %     0.62 g    7.6 m                                          Example 20                                                                            51 mol %     0.98 g    7.8 m                                          ______________________________________                                    

What is claimed is:
 1. A fuel tank of multi-layer construction forcontaining gasoline containing oxygen-containing compounds, whichcomprises:(a) inner and outer layers of high-density polyethylene, (b)intermediate layers of adhesive resin, and (c) a core layer ofethylene-vinylene alcohol copolymer, wherein a ratio (I/O) is less thanabout 40/60,wherein I is the total thickness of the layers positionedinside the layer (c), and O is the total thickness of the layerspositioned outside the layer (c), wherein the layer (c) has a thicknesswhich satisfies the formula:

    0.005≦A/B≦0.13

wherein A is the thickness of the layer (c), and B is the thickness ofall of the layers.
 2. The fuel tank of claim 1, wherein the ratio (I/O)is less than 35/65.
 3. The fuel tank of claim 2, wherein the ratio (I/O)is about 30/70.
 4. The fuel tank of claim 3, wherein the ratio (I/O) isabout 20/80.
 5. The fuel tank of claim 1, wherein the ratio A/B is lessthan 0.10.
 6. The fuel tank of claim 1, wherein the ethylene/vinylalcohol copolymer, comprises ethylene units in an amount of about 20 to60 mol %.
 7. The fuel tank of claim 1, wherein the thickness of the tankis in the range of about 310-10,000 μm.
 8. The fuel tank of claim 1,wherein the ethylene-vinyl alcohol copolymer of core layer (c) has amelt index (MI) in a range of 0.1 to 50 g/10 min at 190° C. under a loadof 2160 g.
 9. The fuel tank of claim 1, wherein the ethylene-vinylalcohol copolymer of core layer (c) has a melt index (MI) in a range of0.5 to 20 g/min at 190° C. under a load of 2160 g.
 10. The fuel tank ofclaim 1, wherein the high-density polyethylene has a density of greaterthan 0.93 g/cm³.
 11. The fuel tank of claim 10, wherein the high-densitypolyethylene has a density of greater than 0.94 g/cm³.
 12. The fuel tankof claim 1, wherein the total thickness of the high-density polyethylenelayers (a) is in the range of about 300-10,000 μm.
 13. The fuel tank ofclaim 12, wherein the total thickness of the high-density polyethylenelayers (a) is in the range of about 500-8,000 μm.
 14. The fuel tank ofclaim 13, wherein the total thickness of the high-density polyethylenelayers (a) is in the range of about 1,000-6,000 μm.
 15. The fuel tank ofclaim 1, wherein the total thickness of the adhesive resin layers (b) isin the range of about 5-1,000 μm.
 16. The fuel tank of claim 15, whereinthe total thickness of the adhesive resin layers (b) is in the range ofabout 10-500 μm.
 17. The fuel tank of claim 16, wherein the totalthickness of the adhesive resin layers (b) is in the range of about20-300 μm.
 18. The fuel tank of claim 1, wherein the ethylene-vinylalcohol copolymer of core layers (c) contains an effective amount of oneor more of hydrotalcite compounds, hindered phenol- or hindered-amineheat stabilizers or metal salts of higher fatty acids, to prevent gelformation.